Thursday, March 5, 2015

Food
must provide fish with the elements needed to "build" their body
(proteins) and the energy (from proteins, carbohydrates, and lipids) required
for its smooth functioning.

Feeding
a fish properly ensures that it will grow satisfactorily, as well as
facilitating its reproduction and helping it to combat disease. Quality and
quantity are two important concepts in feeding: an aquarist must learn to avoid
over-feeding and to diversify the food supply.

AQUARIUM
FISH DIETS AND NUTRITIONAL REQUIREMENTS

With
regard to fishes' feeding habits and dietary requirements, there are three main
groups:

-
Carnivores, which feed on worms, crustaceans, insects, or other fish;

-
Herbivores, with a diet mainly comprising vegetable matter (plants, algae)
which they graze or grind;

-
Omnivores, which have a very varied diet as they eat both animal prey and
vegetable matter. In practice, diets are not always so easy to define. In a
natural setting fish eat what they find, and so sometimes a herbivore will eat
a small animal taking shelter in the plants that it normally eats.

Carnivorous
fish mainly require proteins and lipids, while herbivores have a special need
for carbohydrates, and omnivores demand a mixture of proteins, carbohydrates,
and lipids.

Bearing
in mind the limitations of these definitions, all three diets can be found
among those given to aquarium fish, although there are some exceptions. The
aquarist should also take care that vitamins and mineral salts form part of a
varied and balanced diet, especially through the addition of fresh or live
food.

A wide
palette of foodstuffs stimulates the growth and reproduction of the aquarium's
inhabitants and strengthens their resistance against disease. As such, it is
the best precaution that can be taken against disappointing results and lack of
success.

AQUARIUM
FISH FOOD PORTIONS

There is a tendency to overfeed
aquarium fish and produce some rather flabby specimens. Moreover, there is an
increased risk of pollution in a confined space: the more a fish eats, the more
it excretes nitrogenous substances, and that is without counting the foodstuffs
that quickly decompose in the water in the aquarium.

An adult fish only eats 1 or 2% of its
own body weight per day, although a juvenile consumes twice that amount. Very
light flakes involve little risk of overdosing, in contrast with other
foodstuffs which can sometimes slip out of the hand. Whenever possible, it is
advisable to divide the daily input into separate portions, twice a day for
adults, more often for fry.

As fish in their natural habitat are
unlikely to eat regularly every day, most aquarium fish will therefore cope
well with a short term fast. Some aquarists impose a one-day fast per week to
compensate for the likelihood that the fish have been overfed on the other
days. Fasting is however not suitable for fry as it may slow their growth
considerably.

AQUARIUM
FEEDING WITH ARTIFICIAL FOOD

Flakes of vegetable matter

This is
dry food which is commercially widely available in specialist aquarium stores.
In the last twenty years the entire range has diversified considerably, and
today there is a wide variety, adapted to the needs of different groups of
fishes: for juvenile and adult fish, for freshwater and seawater fish, etc.
These foodstuffs are characterized by a high level of proteins (generally
40-50%) and come in different forms: in flakes (the most common), granulated,
or compressed.

The
flakes float for a while before they sink, which makes them easier to grasp for
surface and openwater fish. There are obviously also different sizes of
foodstuffs, according to the size of the fish's mouth. This artificial food is
fragile and deteriorates if it is not kept in the correct conditions. It must
therefore be stored in a dry place protected from the light. Its composition is
only guaranteed for a certain period, so it is advisable to buy a small box if

flakes for adult heroes

you have only one aquarium and a few fish. Some aquarists do not hesitate to
give their residents trout food, which they buy at fish farms. This food is
very rich in proteins and lipids, thus ensuring the rapid growth of trout bred
for eating, but this not vital in aquariums.

flakes of guppies

Although
such food contains pigments intended to change the flesh color of salmon fish,
aquarists who have used it have not reported any modifications in the external
color of their fish. In any case, this food can prove very economical for
large-scale breeding or garden ponds.

Marine
fish sometimes refuse artificial food, either for a short period after their
introduction to the aquarium, or on a permanent basis. One trick is to
progressively incorporate increasing amounts of commercial food along with
fresh food or live prey. This gradually accustoms the fish to its smell and
taste until they finally accept it on its own.

DIFFERENT
TYPES OF FOOD FOR AQUARIUM FISH

The artificial foodstuffs currently on
the market are very effective for aquarium fish. In order to cover their needs
as fully as possible, fish can also be served small, live prey, which are
similarly available commercially and are an important source of vitamins and
mineral salts. There are other possible options: white meat and mussels, for
example.

AQUARIUM
FOODSTUFFS OF NATURAL ORIGIN

Aquarium
Freeze-dried food

It is
possible to buy freeze-dried food items - small animals, shrimps, worms, or
plankton - in which the water content has been greatly reduced so that they can
be preserved more effectively. This treatment does clearly make them expensive,
but they are at least as nourishing as flakes and very popular with fish. They
must be stored in a dry place. Feed them to the fish according to the
manufacturer's directions and do not exceed the quantities recommended.

Aquarium
feeding with Frozen food

Frozen food:crab andphytoplankton.

Frozen
products - shrimps, fish, worms, and plankton - can also be used, once they
have been separated and rinsed. They have a very high nutritional value, as
freezing does not modify their composition. They are obviously stored in the
freezer and must not be refrozen after thawing, in order to reduce the risk of
microbial contamination. They are more expensive than freeze-dried foodstuffs.

Aquarium
feeding with Domestic food items

Finally,
domestic food can be provided fresh or after freezing and thawing. It is best
to avoid red meats as they have too much fat. Beef heart, rich in both blood
and lipids, can only be given only to large fish. White meats are preferable:
chicken, turkey, or ham. As for seafood, white fish can be used - although it
must be handled with care, as it can break up in the water - as well as
mussels, cockles, and shrimps, which can be bought preserved naturally.
Vegetables are sometimes needed for herbivorous fish: lettuce or spinach that
has been blanched, i.e

Aquarium
feeding with Live Prey

These
are ideal food items for carnivorous fish: they retain all their nutritional
value and move around to attract the fish. They are a problem to keep as they
only last a few days, but they can be frozen.

LIVE PREY
AND HOME PREPARATIONS

The artificial food on the market
these days is very effective for aquarium fish. To diversify and balance their
requirements, they can also be served some of the small, live prey that are
commercially available - an important supply of vitamins and mineral salts - or
fresh food or homemade mixtures.

One of the
best fresh foods: mussels

This mollusk, prized by humans, is
equally appreciated by fish, especially those marine species that refuse
artificial food. Widely available, inexpensive, easy to freeze, mussels are a
top-class dish: they are rich in proteins and carbohydrates, with few lipids.

Furthermore, they contain many minerals
such as calcium, phosphorus, magnesium, iron and even vitamin C, which plays an
important role in the fight against disease. Mussels must be well cooked before
using and their shells and connective filaments removed. Cut them into pieces
before distributing or freezing them.

Aquarium
feeding with homemade food

An aquarist can easily make his or her
own fish food - the possibilities are enormous. The following recipe is just
one of many. Take some cooked white meat (chicken, turkey, ham) and some
seafood (mussels, cockles), also cooked, and mince them with a little water to make
a homogenous paste. A vitamin supplement, available from aquarium stores, can
be added during this process.

This mixture can then be mixed with
gelatin (from a sachet of powder, for example) so that the paste does not break
up in the water, as this may become a source of pollution. One portion can be distributed
immediately, while the rest can easily be frozen in ice trays. The models
designed for small ice cubes are particularly recommended for making a large
number of small portions. Once frozen, they can be slipped out of the ice trays
and bagged up in freezer bags for use as required.

DRIED
DAPHNIAS

These were once very
popular - so many aquarists have started with them! Nowadays they are out of
fashion; in fact they are not the ideal food for fish and it is best not to use
them. More complete and suitable products, particularly those in the form of
flakes, are now available, even for goldfish.

Aquarium
Feeding with Bloodworms

In
fact, these are not worms but the aquatic larvae of various species of
nonbiting mosquitoes. They are also commonly used as bait in fishing. Although
it is sometimes thought that they live in mud, they are actually found in the
water of areas that are well endowed with organic matter. It is useless trying
to collect them yourself, but they are sold in the aquarium trade. They keep
for a few days in the refrigerator, wrapped in moist newspaper. They are a good
source of nutrition, as they are rich in protein.

Aquarium
feeding with Tubifex worms

These
are worms that are gathered from the mud in environments rich in organic matter.
Some people think that they represent a risk when they are introduced into an
aquarium, as they may carry undesirable bacteria. This risk is very slight,
however, and there have been no reports of any serious incidents. The specimens
which are commercially available can be kept for a few days in the
refrigerator, in domestic water, but it is essential that this water is changed
every day.

Aquarium
feeding with Shrimps

Flowing
and well oxygenated fresh water are home to small river shrimps of up 2 cm that
swim along the banks. These are rarely sold live, but they can be found in a
freeze-dried form. You will find that your fish will definitely enjoy them. The
small marine shrimps found on some coasts are also highly prized, especially by
marine fish. These are often sold in fishing stores along the coast. If you are
lucky enough to live in such an area, you can also collect them yourself and
keep them in a well oxygenated seawater aquarium.

Both
types of shrimps can be frozen after being cooked and rinsed under the faucet,
or they can also be ground and turned into a homemade dish.

Feeding
with Small fish

Either
fry or small fish can be used to feed marine fish doubtful about artificial
food, or large freshwater fish. With this in mind, some aquarists breed
prolific species that reproduce easily (Poeciliids, for example).

Other
live prey (larger than 1 cm)

Keeping
and breeding worms or insect larvae is also possible, though it sometimes
proves time-consuming.

The
range of live prey listed above is adequate for the needs of your fish.

Planktonic food

Freshwater
or marine plankton contain a host of organisms barely visible to the naked eye
(0.1-1 cm) but valuable for feeding fish, especially the fry. Collecting them
in a natural setting is tiresome, and involves a risk of introducing potential
microscopic hosts into the aquarium and spreading disease. Some planktonic food
is available on the market in frozen form.

Brine
shrimps

This is
the "magic" food that every aquarist should breed. This primitive
crustacean grows to 1 cm when adult and is called Artemia salina. They
live in the heavily saline waters of salt marshes, feeding on the micro-algae
that they gather with their filtering legs. Their characteristic most relevant
to the aquarist is that their eggs can be stored dry, with their development
interrupted, for use later on. Once the eggs are returned to salty water, they
hatch rapidly and produce a larva called a nauplius,
which measures only 0.3 mm and is particularly suitable for feeding to fry.

Feeding
brine shrimps to fish is easy, even for an amateur (see box). They are still
too big for the fry of some fish, however, especially marine species. In such
cases, it is possible to use rotifers, animals halfway between worms and
crustaceans, which have a crustacean-like shell and never grow to more than 0.2
mm.

Rotifers

These
are more complicated to breed than brine shrimps, as they must be fed
planktonic micro-algae which also need to be cultivated. It is therefore best
to obtain them from a laboratory specializing in oceanography or marine
biology, and to get advice on the essential steps required to look after them
for a few days – the time within which the fry for which they are intended will
be big enough and sufficientlysufficiently
developed to move on to a diet of brine shrimp nauplii.

Aquarium
Food Distribution

When
they are healthy and well-adjusted to captivity, fish eat at a regular time and
become accustomed to the spot where the food is given out. It is advisable to
divide the daily ration into two parts - one in the morning and one in the
evening, for example. The end of the day - 1 or 2 hours before turning the
aquarium lighting off - is usually the most practical for the aquarist. In any
event, food distribution offers a special opportunity to observe the behavior
of your residents and check their state of health.

Allowing
the fish to come and feed out of your hand is particularly enjoyable, but take
care, because some large specimens have impressive teeth! If the water is too
agitated, artificial or natural food may be dispersed too quickly and washed to
a corner of the aquarium where the fish will not be able to recover it. Thereby
creating a potential for pollution. The stirring of the water must therefore
cease when food is being distributed and eaten.

Feeding
the fry

When
they are born, the fry of egg-laying fish feed on the reserves in their
vitellin vesicle, as their mouth does not open until a few days later. They
will then often accept the fine powders which are available commercially. If
this is not the case. Give them brine shrimp nauplii for a few days – newly
hatched nauplii are most suitable for the first two days. After that, they can
be offered nauplii that are 48 hours old.

Daily
production over a period of several days must therefore be planned for. If
brine shrimps are unavailable, another option
is the production of infusorians. Live-bearing fish (the Poeciliid family)
accept artificial food from birth, and they also thrive on brine shrimp
nauplii. As for marine fish, rotifers, discussed above, should be used, as they
easily fit into the small mouths of the fry.

BREEDING
BRINE SHRIMPS

The dry eggs (known as cysts) are
available in aquarium supply stores. They must be kept away from light and
moisture. In order to make them hatch, salt water must be prepared with the
following characteristics: temperature 25°C, salinity

35%, i.e. a specific gravity of 1.023.
The salt water can be natural or reconstituted with special aquarium salts, or
even with rough kitchen salt (easier for aquarists who do not keep marine
fish).

The water can be colder and less salty
(up to 20°C and 20%, i.e. a specific gravity of 1.014), but the hatching rate
will be lower (50-60% against 80-90%). Any small glass or PVC container can be
used - bottles, for example - although specialist equipment is available. The
eggs are placed in the still water for a quarter of an hour, the time required for
their rehydration. If we estimate that 250,000 eggs weigh around 1 g, a tiny
amount (the tip of a knife, for example) will produce sufficient brine shrimps.

Aerate the water slightly to produce
small bubbles, which will disperse the eggs, but be careful not to stir the
water too vigorously, otherwise some of the eggs will crash against the sides
of the container and will not hatch. The hatching occurs after 24 36 hours at
25°C, or after up to 48 hours at 20°C.

Finally, switch off the aeration: the empty
shells will float to the surface, the unhatched eggs will fall to the bottom,
and the brine shrimp nauplii will be swimming just under the surface. It is
then easy to siphon them off (with an aeration pipe, for example) and strain
them through a small filter (available commercially), or, alternatively, through
the thin mesh of a piece of old curtain, or even a very fine pantyhose. To make
this operation easier, you can group the nauplii together using a flashlight,
as they are attracted by light. You can then go on to feed them to the fry.
They will only survive for a few minutes outside salted water, and they will
not eat on the first day after hatching.

If you want to keep them for several
days to obtain larger or more mature larvae, special food is commercially
available. This makes it possible to keep brine shrimps until they are adults this
operation easier, you can group the nauplii together using a flashlight, as
they are attracted by light. You can then go on to feed them to the fry. They
will only survive for a few minutes outside

ADULT
BRINE SHRIMPS

Adult brine shrimps are sold live in
small sealed sachets containing salt water and air. They are passed through a
sieve before being given to the fish, which enjoy hunting them down. They
survive for a few minutes in unsalted water. Brine shrimps can also be bought
frozen.

When
feeding, it is important to avoid any overdosing, whether with artificial food
or live prey, such as the adult brine shrimps pictured here.

Infusorians

These
are microscopic, unicellular animals, easy to produce in fresh water. They are
usually present in small numbers in an aquarium. Riccia, a surface plant, gives
them a chance to grow, as they find food (organicmatter) on its leaves. They
can also be produced by leaving a piece of potato, a lettuce leaf, or some
paddy rice (unhusked rice, available in grain stores) to soak in a receptacle
containing aquarium water.

What
if a fish does not eat?

Sometimes
a fish refuses to eat, or appearsto be incapable of doing so. It is
thereforea question of finding the cause and eliminatingit. A
newcomer to a tank rarely eatson the first day. This is normal, as it
feels lost in its new environment. Small species and more lethargic fish are
often dominated by their bigger and faster cohabitants at feeding time.

They
must therefore always be fed separately, preferably with mobile, live prey,
once the other fish have been distracted by other food. A fish can also refuse
to eat if it is sick, and this will be reflected in its behavior, color, and
other symptoms which may eventually be seen on its body. In this situation it
must be isolated in another aquarium, treated, and given rich food. Comprised
of live prey or fresh produce. Sometimes fish can systematically refuse to eat
artificial food, although this is rare in fresh water, but less so in marine
aquariums. There is no point in being stubborn: change to a varied diet based
on live prey and homemade fare.

GOLDEN
RULES FOR FEEDING AQUARIUM FISH

-Give fish a varied diet;

-Give them a little, but often. Two portions a
day is ideal. For fry, the feeding can be more frequent.

-Do not wait until the fish are sated and stop
eating. Stop feeding once the ration is complete;

-Siphon off any food surplus as quickly as
possible, as the leftovers are pollutants.

A
MIRACLE FOOD FOR FRY

A hard-boiled egg yolk is
added to water in a glass. This forms microparticles which are then sieved.

This nutritious liquid is
then given to the fry, taking care not to put too much into the tank, as it is
always important to minimize pollution. Egg yolk, rich in proteinsm and lipids,
can be used as a complement or as a replacement for other food.

Aquarium fish Anatomy & Biology

There are more than 30,000 species of fish, more or less evenly distributed
between fresh water and sea water, and of these some 1,500 are of interest to
the aquarist. Fish embody a great anatomical and biological diversity and
richness, and this can be clearly seen in aquariums.

Whatever
type of aquarium you choose, a minimal knowledge of the anatomy and biology of
the species you are raising is an essential prerequisite. The information
below, presented in layman's language, allows you to keep your fish in good
health, in the best possible conditions, to feed them appropriately so that
they can grow, and to facilitate their reproduction — in short, to understand
them better in order to take better care of them.

External Anatomy of a fish

The
body

A fish
is typically drawn as an elongated spindle, and in fact this is the most common
form, as it makes it easier to swim in open water. These hydrodynamic
characteristics permit rapid acceleration and not inconsiderable speeds
(sometimes up to 20 km per hour) in a medium (water) that offers a certain
degree of resistance.

However,
there are other forms that are also all connected with the lifestyle of the
fish in question: bottom- dwellers have a flat stomach, while those that live
in water obstructed by plants and branches have compact, thin bodies that
enable them to squeeze through the obstacles. This is equally the case with the
countless fish in the coral reefs, which thread their way through the blocks of
coral. Finally, there are certain fish that are unclassifiable, so varied and
strange are the forms they flaunt, although they always correspond to a
particular lifestyle.

The
fins of a fish

Fish
have several types of fins, each one playing a precise role. Their forms and names
are often used to classify them into different families. Of the unpaired fins
(i.e. consisting of a single fin), the most noteworthy are the dorsal and the
anal fins. These serve to stabilize the fish when it is not going very
fast or is coming to a halt, and they are tucked in when the fish swims more
quickly.

The
caudal fin (incorrectly referred to as the tail) supplies propulsion, in
conjunction with the rear part of the body. In some species, particularly the
Characins and the catfish, there is a small extra fin between the dorsal and
the caudal fins, known as the adipose fin.

The
paired fins, attached symmetrically to each side of the body, are called
pectoral and pelvic fins. They are used for stabilizing, stopping, slowing
down, or changing direction: vertically, from the water surface to the bed, and
vice versa, from side to side, from left to right, from right to left. Fins
consist of a membrane stretched on spokes, and they can all be tucked in along
the body, with the exception of the caudal fin. The adipose fin is merely a
fold of skin, without any spokes. When the spokes are longer than the fins they
are known as spiny fins, and they can represent a danger to the aquarist, as in
the case of the scorpion fish, for example.

The
mucus, skin, and scales of a fish

Fishes'
bodies are covered with a mucus that plays a double role: it reinforces the
hydrodynamics by "smoothing" the skin, and it affords protection
against the penetration of parasites or pathogenic elements. The latter point
is extremely important, and it explains why fish must not be moved by hand:
this risks damaging the mucus and facilitating the development of certain
diseases.

SPECTACULAR
FINS MAY BE NURTURE NOT NATURE

Some aquarium fish have fins that are
very different in shape or size from those that are found in nature. They are
the result of patient breeding carried out by aquarists over a period of years.

The visual effect is guaranteed, but
the fish's behavior is sometimes altered, especially its velocity when moving
around.

Fish with large fins in the form of
sails have little more than a remote relationship with their wild cousins,
which have gone out of fashion and are no longer to be seen in tanks. The
purpose of these selections can sometimes be in doubt: they undeniably result
in highly attractive fish, but what advantage do they have over other stunning
natural specimens?

Contrary
to a widely held belief, the scales do not stick out of the body but are an
integral part of the skin, and they are visible through a fine layer of
transparent epidermis. When a scale is raised, damaged, or torn off, the skin
itself is equally affected and becomes vulnerable to the action of pathogens.

Coloring
of a fish

Every
fish has a basic coloring that can be modified. Their shiny, metallic
appearance, derived from the crystals present in the cells of the skin, varies
according to the direction of the light striking them. A fish's color is a
result of the different pigments located in the epidermis. These can change,
slowly, for reproduction and camouflage, under the control of hormones, or more
quickly, for flight or aggression, controlled by
nerves. The coloring of a fish can also vary when it is suffering from
disease or nutrient deficiency.

COLORING:
PROTECTION, WARNING, AND SEDUCTION OF A FISH

The coloring of a fish varies
according to its age and mood. Some fish living in coral reefs

rejectindividuals of their own species ora related
species with a coloring similar to their own (Pomacanthids, also known as
angelfishes, for example) because they consider newcomers as enemies wishing to
appropriate their territory and their food supply. This is why their offspring
have a very different coloring from that of adults, so as not to be considered intruders.
In their desire to protect themselves, some fish adopt a camouflage to merge in
with their surroundings, or, in contrast, reduce the intensity of their color
to pass unnoticed.

Thus, the vertical black stripes on
the scalare allow it to hide among submerged branches and plants (see drawing
above). In some species, the male and female sport very different colorings, enabling
them to be distinguished - a gift of nature much appreciated by aquarists!

This is true of a large number of the Cichlids
in the African lakes. At mating time, the male can flaunt vivid colors, not
only to seduce the female in the courting ritual but also to impress his rivals
and scare them off. This occurs with the meeki, a Central American Cichlid -
the underside of its head turns red at mating time.

The
head of a fish

Whatever
its form - conical, elongated, or stocky - the head houses some important
organs: - first of all, there are the eyes, which have no eyelids and
are highly mobile. This mobility, coupled with their position on the side of the
head, allows a fish to command a broad field of vision - around 270°. In
contrast, the clarity of its vision is unexceptional: beyond a certain
distance, it distinguishes masses and forms rather than details.

Fish
are very sensitive to variations in light - detecting low intensities of light,
such as that of the moon - and they can recognize colors. - Next comes the
mouth, with a size and shape related to its feeding habits. Carnivorous fish
generally have a large mouth that can open wide and is endowed with an array of
pointed teeth, which are sometimes curved towards the back to keep hold of
their prey. Omnivorous and herbivorous fish have a smaller mouth, with flat
teeth ideally suited to grinding food. The position
of the mouth cansimilarly
reveal eating habits:

• A
mouth in the upper position indicates a top-feeder;

• A
mouth in the terminal position is the sign of a fish that hunts underwater;

• A
mouth in the lower position indicates a bottom-feeder.

How
fish breathe

Water
is aspirated through the fish's mouth, passes through the branchiae and is expelled
due to the movements of the operculum, which covers them. There is always some
water washing the branchiae of the fish. Oxygen requirements are not directly
proportional to the size of the fish, with the smallest species being the
greatest consumers of oxygen: ten fish weighing 1 g each consume more oxygen
per gram of body weight than one fish of 10 g.

The
barbels of a fish

Fish
that live on the bed or in dark environments (colored or turbid water) have
barbels around the mouth (Corfdoras,Botia, for example). These
appendages have a tactile and sensory role. By complementing or replacing the
eyes, they enable the fish to detect possible sources of nutrition.

The
nostrils of a fish

Two or
four in number, these are located in front of the eyes. They play no part in
respiration but, extended inside the head by an olfactory sac, they perceive
and analyze smells.

The
operculum of a fish

This
protects the branchiae and guarantees the circulation of water through the
regular movements of

The
valve, ensuring that the branchiae are always in contact with the water from
which they extract oxygen.

The
term "gills" sometimes incorrectly used,
refers to theopening
produced by the movements ofthe
operculum, which serves as an exit forthe
water that has irrigated the branchiae.

The
lateral line of a fish

Running
symmetrically along each side of the fish's body, the lateral line is more or
less visible, according to the species. It consists of a succession of pores
that communicate with a canal situated under the skin. This important organ
does not exist in any other vertebrates.

While
the senses of taste and smell, highly developed in fish, allow them to
recognize a greater number of smells than humans, at very low concentrations,
the lateral line, with its special cells, detects and analyzes the vibrations
of the water and sends this information to the brain. In this way a fish can be
aware of the proximity of an enemy, of a prey... or of the approach of the
aquarist (see box, p. 47). The importance of the lateral line is apparent in
the blind tetra (Anoptichthys jordani), which never bumps into anobstacle
even though it has no eyes.

Internal
Anatomy of a fish

The sum
of the internal organs accounts for roughly 50 to 60% of the body weight in a
classically shaped fish.

The
brain of a fish

This is
fairly simple in fish, when compared to other more evolved animals. The parts
corresponding to sight and smell are particularly well developed, demonstrating
the importance of these two senses.

The
fish skeleton

Obviously,
this supports the fish's body, but it is less sturdy than that of a land
animal, as a fish, partially freed from gravity, is "carried" by the
water. Nevertheless, the relative fragility of the skeleton is a handicap and
it is not uncommon to find fry that emerge from their egg "twisted".

The
fish respiratory and circulatory system

This
system is highly distinctive. The blood loaded with carbon dioxide is pumped by
the heart to the branchiae, where it is oxygenated. Nature has provided fish
with eight branchiae (four on each side), each made up of two leaves. The total
surface area of these essential organs, when spread out, would be nearly equal
to that of the fish's body.

The
vivid red color of the branchiae is due to their abundant irrigation of blood;
a darker color is a symptom of a respiratory problem. The branchiae are fragile
organs, susceptible to damage from suspended sediment or parasites, resulting
in a reduced intake of oxygen, with all its unfortunate consequences. After
traveling through the branchiae, the vivid red blood, rich in oxygen, irrigates
the body, and the oxygen goes on to break down the foodstuffs I the organs.

The
fish in the Belontiid family, which live in water in which the oxygen is
sometimes rarefied, have a special organ for trapping atmospheric oxygen.

The
fish digestive system

This
has no special characteristics, apart from the fact that the stomach can
stretch to hold large prey, especially in carnivorous fish. This is where
digestion starts, and it then continues in the intestine. With large prey the
process can last several days, but in an aquarium, with artificial food, it
will not take more than a few hours.

The
fish excretory system

This
allows undigested matter to be evacuated through the anus in the form of
excrement, or feces. The urine is formed

in the
kidneys, situated under the spinal column; it is evacuated through the urinary
pore. It is worth mentioning that fish also excrete nitrogenous
substances via the branchiae. All excreted substances contain nitrogen and are
toxic for animals, but in a well-balanced aquarium they are eventually
converted into nitrates and thus because no harm.

DO
FISH RECOGNIZE THEIR OWNER?

Countless aquarists have noticed that
some of their fishes react more enthusiastically to their presence than to that
of strangers. If they do "recognize" the person who looks after them,
how do they do it? They are capable of distinguishing the special
characteristics of the vibrations caused by the footsteps of such and such
person, which are transmitted to the water of the aquarium. Not only has that,
their sense of sight, although not perfect, helped them in this task of
"recognition."

Which
of the two recognizes the other first? •

The
swim bladder of a fish

Fish
have a swim bladder, also known as an air bladder. This is an organ connected
to the digestive system, which fills up with gas and helps fish to regulate
their flotation when moving between two different types of water. They empty it
to dive and fill it up when they need to come nearer the surface.
Bottom-dwelling fish generally have asmaller swim bladder, or none at all, as
they rarely swim in open water.

The
reproductive organs of a fish

Males
have two testicles that are linked to the vas deferens. While females have ovaries
extended by the oviducts. In both cases the sexual products - the spermatozoa and
ova - are expelled via the genital orifice. As the fertilization of the eggs is
external and takes place in the water, there are no organs for coupling and
fertilization, except in the case of livebearers.

DO FISH
SLEEP?

When an aquarium is abruptly switched
on in the morning, it is noticeable that its occupants do not immediately
resume their normal activity. Some of them are on the bottom of the tank, some
in the plants, and others remain almost immobile in the water. It is difficult
to speak of sleep in the generally accepted sense of the word, but it is
certain that fish have periods of restfulness, of varying degrees. This can be
verified at night, with the aid of a small flashlight: the fish are practically
stationary (apart from nocturnal species), but their eyes are not closed as
they have no eyelids.

DO FISH FEEL
PHYSICAL PAIN?

The sensation of pain is sent to the
brain via the sensory nerves. As fish are endowed with the latter, it can be
assumed that they feel pain when they are hit or wounded, and perhaps even when
they are sick.

FISH
BIOLOGY

How
do fish swim?

It is
essentially the rear part of the body, particularly the caudal fin, which
serves to propel the fish, while the other fins play a stabilizing and steering
role. Of course, the more hydrodynamic a fish's form, the more it is capable of
setting off abruptly and swimming quickly, indispensable for catching prey or
fleeing an enemy. Aquarists are sometimes advised not to let quick and lively
fish (like Barbs) cohabit with slower and more placid species (like loaches),
as the latter may be frustrated in their attempts to eat the food provided by
their owner.

General
Fish Behavior in Aquarium

Fishes'
behavior in an aquarium reflects their lifestyle in a natural habitat, albeit
modified by the fact that they are living in a more cramped environment, coming
into contact with other species more quickly and easily. Fish from the same
species can behave differently from one aquarium to another, according to th
capacity and the other occupants.

• FishTerritorial
behavior

When
fish are in their original biotope, their territorial behavior is reproduced in
captivity, and is sometimes even intensified. A territory is a living space –
either permanent or temporary (as in the reproduction period) - with an
extension proportional to the size of the fish. Its occupant rebuffs
individuals from the same species, from related species, or even from totally
different ones. The surface area must be sufficient for the fish to find
refuge, foodstuffs, and fish of the opposite sex with which to reproduce. With
some fish, particularly marine species, it is important to plan a territory in
the aquarium that will provide shelters and hideaways.

• FishGroup
behavior

Strength
is to be found in unity, and living in a group permits a better defense against
enemies. Indeed, from a distance a group or school of fish takes on the
surprising and intimidating an enemy.

Group
life also facilitates reproduction, as an individual has a greater chance of
finding a fish of the opposite sex. A group's unity and organization are
governed by a series of signals which are invisible to human eyes: the use of
the lateral line, for example, prevents fish from colliding with each other.

• FishDominance
behavior

The
biggest members of a species dominate the smallest ones: when the latter get bigger
they are ejected from the territory. Dominance behavior has practical and social
implications, as the dominator will have priority in food and the choice of a fish
of the opposite sex. At the bottom of the social ladder, the most dominated
fish is permanently subject to aggression and harassment and has to hide most
of the time, with its growth being prejudiced as a result. This is the case
with some species of African Cichlids.

• Prey-predator relationships of fish

Some
fish feed on other smaller ones in a natural habitat, giving rise to
incompatibilities in an aquarium: take care, for example, not to let South
American Cichlids cohabit with Characins.

• Aggression

Sometimes
an aquarium is a stage for aggression between different species. This
aggression is always justified, as it is related to the defense of territory or
offspring. It is a problem of space – these phenomena are rarely seen in big
aquariums. However, a new fish introduced into a tank will often be considered
as an intruder, or prey, and will be harassed.

Fish
Growth and longevity

Unlike
human beings, fish continue to grow throughout their life, quickly at first,
and then more slowly with age. The size of fish in aquariums is mostly smaller
than that found in the wild, undoubtedly as a result of the restricted living
space at their disposal. This can easily be put to the test: an individual
whose size has seemingly stabilized starts to grow if it is put into a bigger
tank.

As
regards longevity, this varies according to the species: a year, more or less,
for the small species, and two to five years for the majority of fish. Some
patriarchs live to the ripe old age of ten or more - these are large fish,
particularly marine species. It is very difficult to postulate an optimal life
span for a given species in captivity, as environmental conditions introduce
too many variable factors.

In
nature, the biggest fish often feed on smaller ones – obviously something to
avoid in an aquarium.

HOW
TO REDUCE ACTS OF AGGRESSION

IN
AN AQUARIUM?

Only put together those
fish which are known to be compatible, particularly in the case of marine fish,
and give them as much space as possible. Be sure to provide a number of nooks
and crannies, appropriate for the dimensions of the residents. Another solution
is to mix species with different lifestyles – for example, free swimmers (like
Barbs and Danios) and bottom dwellers (like loaches) - that will not compete
with each other.